Although built-in validation support in Spring is largely sufficient for standard use cases, sooner or later you will run into a situation when the sets of validation annotations provided by JSR 303 or Hibernate Validator aren’t enough. In this post you will learn how to create a simple constraint annotation served by a custom validator with access to the Spring context of a Spring Boot application.
All built-in JSR 303 constraint annotations are intended to verify particular fields of our data classes. Yet, it is not unusual that several fields are connected to each other and should be checked as a unity. For instance, a field can be required only if another field is set. @NotNull won’t work in such case as there is no way to introduce the condition logic. In this post you will learn how to write a validator applicable to multiple class fields.
Some validation constraint can be applied to several different types. For instance the @Size annotation works with collections, arrays, and strings. This post is a guide on how to create a validation constraint which can be applied to different data types just like the aforementioned @Size annotation.
In the previous post you could learn how to create a basic custom constraint annotation compatible with the Bean Validation standard. This demo will extend the former post by explaining how to create constraints which are more flexible due to parameters defined for particular use cases. If you’re totally unfamiliar with the topic, I refer you to the aforementioned post to grasp the essentials. Otherwise, just keep reading.